Radio frequency (RF)-shielded rooms and SCIF areas are primarily constructed and used by the military and the government to create secure areas where computing and various forms of communications can occur without those areas being susceptible to outsiders intercepting the secret information or communications occurring therein. Computers and other electronic devices create electrical emanations that can be transmitted over power lines, communications lines, and other electronic cables that are resident in a SCIF. As a consequence, communications and computations can be intercepted and interpreted.
RF-shielded rooms are constructed using steel (or copper) walls and electronic filters and re connected to power and communication cables to isolate the electrical emanations created by the computer equipment and communications equipment within the SCIF. Unfortunately, electronic filtering techniques that are used on incoming and outgoing power and communications cables prevent most types of fire alarm circuits and other two-way communication paths from properly functioning within SCIF's.
SCIF areas are also constructed to protect against speech conversations from being intercepted or heard outside the secure area. SCIF areas are also built to protect from speech conversations being “heard” by passive speaker circuits (such as public address systems, fire alarm voice speaker circuits, and intercom systems). These small electrical currents can be intercepted on the system cabling outside the secure area and be amplified to actually “listen in” on the private conversations. Generally, speaker circuits for public address systems, intercom systems, and fire alarm systems are not built to prevent this compromise of voice information. If speakers having countermeasures were in place, they might not meet the requirements for audible alarm systems.
Thus, the regulations that allow a SCIF to be qualified to house classified operations are frequently at odds with meeting building code requirements for providing proper audibility of fire alarm signals in the secure areas of the building.
Fiber optical cabling offers a secure means of communication that is generally immune from electromagnetic interference and eavesdropping. While these qualities of fiber optical cabling have been exploited in the art, the use of such cabling to provide alarms in secure areas has not been addressed.
In U.S. Pat. No. 4,161,650 issued to Caoutte et al., fiber optical cable is used to convert the output of a parallel electrical interface to optical digital signals, and to convert the optical digital signals back to parallel electrical signals at the receiving end. The fiber optical cable was identified as reducing cross-talk over copper circuits.
In U.S. Pat. No. 4,596,049 issued to Rizzotti, digital control signals are sent over fiber optical cable between a plurality of remote stations and a local control station. The local control station monitors a device to be controlled and reports on its status to the remote stations. The fiber optical cable was identified as reducing EMI, particularly in control circuits used on ships.
In U.S. Pat. No. 5,724,363 issued to Breya, a system and method for reducing system errors in an amplitude modulated optical signal transmission system is described. The invention is directed to calibrating a selected analog optical channel while transmitting on another analog optical channel.
In U.S. Pat. No. 4,839,527 issued to Leitch, a fire detection system uses fiber optics to detect communicate the presence of smoke, and to analyze the chemical composition of the smoke.
In U.S. Pat. No. 4,933,667 issued to Shaw et al., a graphic annunciator is described. In a preferred embodiment, the annunciator includes a plurality of light-emitting diodes arranged in a graphic representation of the protected area and a signal processor coupled with the light-emitting diodes for receiving and processing the data signals and for selectively actuating the light-emitting diodes in response thereto according to configuration data stored in memory. The data signals are preferably optical signals transmitted over a fiber optical cable.
In U.S. Pat. No. 5,999,094 issued to Nilssen, a multiconductor telephone and smoke alarm distribution system is described. In an embodiment at least some of the conductors are fiber optical cables with the state desire of attaining a high degree of electromagnetic separation.
In U.S. Pat. No. 4,533,834 issued to McCormack, a fire detection system using optical fibers to transmit flame signals from a plurality of remote monitoring stations to a central detection and analysis station is described. Light from the fibers being dispersed by a prism associated with the scanner to allow detection of the various spectral components of the dispersed light by light sensitive semiconductors. The detected spectral components are then compared to known fire signal signatures which include flicker rate and spectral content information.
In U.S. Pat. No. 4,174,149 issued to Rupp, a secure communications system is disclosed which utilizes an optical signal transmitted over a frangible optical fiber. An alarm signal is continuously transmitted from the information receiver site to the information transmitter site over the same optical fiber. Any attempt to penetrate the optical fiber for the purpose of intercepting the information transmitted therein causes the frangible fiber to shatter, thereby disrupting the alarm signal being received at the information transmitter site. The detection of this condition results in the immediate disabling of the information transmitter
What would be useful would be a system and method for securely communicating an alarm condition in a safety related system (SRS) occurring outside of a SCIF to the occupants of the SCIF and for securely communicating an alarm condition occurring in a SRS inside a SCIF to a location outside the SCIF. Such a system and method should provide for detection of the failure of an SRS within the SCIF.